Science and sun worship

Updated 10:28 pm, Monday, June 18, 2012

Revelers watch the sun rise over Stonehenge on Salisbury Plain, England, on the summer solstice.

Revelers watch the sun rise over Stonehenge on Salisbury Plain, England, on the summer solstice.

Photo: Matt Cardy, Getty Images

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To mark the summer solstice, thousands of people dance, blow bubbles, build bonfires and watch the sun rise each year at Stonehenge.

To mark the summer solstice, thousands of people dance, blow bubbles, build bonfires and watch the sun rise each year at Stonehenge.

Photo: Matt Cardy, Stringer

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Michael Barnes, 11, experiments with the Cockrell Sundial at the Houston Museum of Natural Science. The museum invites the public to observe the summer solstice Wednesday with some solar experiments.

Michael Barnes, 11, experiments with the Cockrell Sundial at the Houston Museum of Natural Science. The museum invites the public to observe the summer solstice Wednesday with some solar experiments.

Photo: Cody Duty, Staff

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An image of the sun is projected through a lens atop the Cockrell Sundial at the Houston Museum of Natural Science. The museum invites the public to try this trick at a Wednesday-afternoon solstice event.

An image of the sun is projected through a lens atop the Cockrell Sundial at the Houston Museum of Natural Science. The museum invites the public to try this trick at a Wednesday-afternoon solstice event.

Photo: Cody Duty, Staff

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At the summer soltice, an image of the sun can be captured by a lens atop the Houston Museum of Natural Science's Cockrell Sundial.

At the summer soltice, an image of the sun can be captured by a lens atop the Houston Museum of Natural Science's Cockrell Sundial.

Photo: Cody Duty, Staff

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At Stonehenge in England on the summer solstice, the sunrise is perfectly aligned with the outer Heel Stone. Thousands gather to watch it and celebrate the sun on the longest day of the year.

At Stonehenge in England on the summer solstice, the sunrise is perfectly aligned with the outer Heel Stone. Thousands gather to watch it and celebrate the sun on the longest day of the year.

Photo: Matt Cardy, Stringer

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Thousands gather for an all-night party each year at Stonehenge to mark the summer solstice. They stay to watch the sun rise early in the morning.

Thousands gather for an all-night party each year at Stonehenge to mark the summer solstice. They stay to watch the sun rise early in the morning.

Photo: Lefteris Pitarakis, STF

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Science and sun worship

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On Wednesday, we reach the summer solstice. The first day of summer. The longest day of the year.

It's scientific: The solstice is an astronomical event, a day of solar significance. It's also spiritual: Around the world and throughout history, rituals and celebrations have been tied to the solstice.

As we prepare for a long, light-filled day, here's a look at what the summer solstice is all about.

The science

The summer solstice is the longest day of the year because it has the longest period of sunlight: In San Antonio, the sun rises at 6:35 a.m. and doesn't set until 8:37 p.m., giving us more than 14 hours of light.

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What causes the solstice?

The Earth is always tilted on its axis at 23½ degrees, Sumners said. It orbits around the sun in that position - and in the Northern Hemisphere, when that tilt leans toward the sun, we call it summer. "We are reaching that point in the Earth's orbit where we are tilted most toward the sun," Schlegel said. And when we get there, that's the summer solstice.

So will the sun be directly overhead Wednesday?

Nope - not in San Antonio. At the Tropic of Cancer, a line around the Earth that hits just north of Cuba, the sun will be directly overhead. For a brief time there - and only there - on Wednesday, nothing will cast a shadow.

We're too far north to witness that phenomenon. We'll come closest, though, at "solar noon," when the sun is highest in the sky. That'll happen at 1:34 p.m.

Doesn't the sun know that noon is at 12 p.m.?

It's an hour later because of Daylight Saving Time, which is in effect this time of year. And on top of that, San Antonio is about 34 minutes west of the time-zone meridian. In other words, the sun gets to us 34 minutes later than it does to the folks on the eastern edge of the Central Standard Time zone. We're always just a few minutes behind the time our watches display.

What does the sun's position mean for us?

It means a lot of intensity. "The higher the sun is in the sky, the more solar radiation we get," Sumners said. "You'll get your quickest sunburn on the summer solstice - the sun is most intense." In other words, wear some extra sunscreen.

Isn't the solstice usually June 21?

Yes, but it's June 20 this year. That's a calendar thing, Schlegel said. The Earth takes 365¼ days to orbit the sun. That's why we have leap year every four years, including this one. And that means there are adjustments to the calendar that will occasionally throw the solstice off a day.

The spiritual

Why is the solstice a spiritual time?

"Certainly, the longest day of the year has been recognized around the world in spiritual and religious traditions," Whitehurst said.

For many cultures, the solstice was a celebration of agriculture - acknowledgment of the sun's role in growing crops. It also marked the passing of the sun, which had reached its peak for the year. Even today, to mark the solstice is to acknowledge that the days will get shorter now and winter is on the way.

For the ancient Egyptians, the solstice generally marked the start of the Nile's flooding season, when the river overflowed its banks and enriched the soil. The Incas celebrated Inti Raymi, the multiday Festival of the Sun, to mark the solstice. The ancient Greeks, too, celebrated with festivals - and they scheduled the Olympic games to begin after the event had come.

Do people still celebrate the solstice?

Absolutely. In the United States, summer solstice parades and festivals are scattered across the country, including Seattle, Santa Barbara, Calif., and Long Island City, N.Y.

England is home to the most famous celebration: Each June, thousands gather at Stonehenge the night before the summer solstice. They wait all night for the sun to come up over the stone monument; it lines up perfectly with the outer Heel Stone.

There's dancing. There are bonfires. Why such a celebration at Stonehenge? In that part of the world, the seasons are sharply different, Sumners said.

"The more north you are, the more you care about the sun being high in the sky," she said. "When the sun is highest in the sky in Britain, the difference is dramatic."

Even in Texas we'll find ways to worship the sun Wednesday. And we see plenty of it down here.